I. Field of the Invention
This invention relates generally to medical apparatus for monitoring physiologic parameters within the body of a human or other animal, and more particularly to an implantable device for chronic monitoring of pressure, flow and temperature within living humans or animals.
II. Discussion of the Prior Art
In the diagnosis and treatment of various maladies, a variety of devices have been developed which can be implanted within the body and used to monitor various physiologic parameters. With the advent of microminiature circuitry, it has become practical to implant a variety of sensors responsive to various physiologic changes, along with circuitry for the transcutaneous transmission of information from the implanted unit, via a telemetry link to an external recording/display device. For example, in the field of implantable cardiac pacemakers and defibrillators, sensing circuitry is incorporated therein for monitoring a number of physiologic parameters, such as respiratory rate, tidal volume, heart rate, blood temperature, movement, etc. Pacemaker leads have been developed that incorporate pressure transducers and temperature sensors such that the pacing rate of the implanted device can be made to vary in relation to detected changes in blood temperature and blood pressure.
In implementing such devices, the electronic circuitry is housed in a body compatible, fluid impervious housing along with a suitable power supply or AC to DC converter and electrical leads are then routed from the implant site and through the vascular system to a location on or in the heart. Because of concern that the presence of a lead in the left ventricular chamber may result in the formation of a thrombus that could break loose and reach the brain and cause stroke or embolize to another peripheral vessel, pacing leads or other devices are seldom inserted into the left ventricle, especially for chronic monitoring or therapy delivery.
The ability to measure left ventricular pressure or its surrogate in the ambulatory patient, non-invasively, has great potential in determining the status of heart failure patients, providing an opportunity to modify medical management of ventricular dysfunction very precisely as compared to current clinical practice. Moreover, ambulatory hypertensive patients can be managed more closely when peak systolic and diastolic pressure can be chronically monitored.
The ability to measure myocardial temperature with an implanted device and to thereafter telemeter the temperature information to an external monitor will permit cardiac transplant patients to be closely managed. It is believed that rejection in organ transplant patients manifest early as a small tissue temperature elevation due to the inflammatory reaction of rejection. The only presently available method to determine transplant status is to perform a biopsy, an invasive procedure that is sometimes done weekly or more often, and is done in such a patient hundreds of times during that patient""s life. A device for measuring tissue temperature and telemetering the information to an external monitor would limit the number of times such biopsy is requiredxe2x80x94a significant clinical advance.
Myocardial temperature sensing is beneficial in the management of heart failure. Ventriculo-vascular coupling and impedance mismatches manifest themselves as excess heating of the ventricle. By having temperature monitoring available, accurate titration of preload and afterload reducing medication could be achieved to limit myocardial energy output and thereby the heart will perform more efficiently. Therefore, a need exists for a system for chronically monitoring temperature and pressure within the left ventricular and/or atrial chambers of the heart or myocardial tissue.
It has also determined that a temperature sensor located in the pulmonary artery branches for sensing lung tissue temperature can provide meaningful information following heart/lung transplant surgery in that an elevated blood or lung tissue temperature in the pulmonary artery or branches may be indicative of the onset of rejection, allowing interventional adjustment in the amount of anti-rejection drug being administered to, the patient. We are presently unaware of any temperature sensor that can be chronically implanted to measure temperature changes in blood traversing the pulmonary artery.
By locating the monitor implant at other locations within the body, renal, hepatic or pancreas transplant status can be assessed. Locating the device in the peripheral blood vessels can allow assessment of exercise capacity. The monitor may also be used to calculate blood flow using thermodilution techniques.
From the foregoing, it can be seen a need exists for an implantable sensor especially designed for placement in a selected portion of a patient""s vascular system and which can be used to chronically transmit pressure and/or temperature data to an external monitor/display unit so that a medical professional can more readily diagnosis and treat various medical conditions. It is principal object of the present invention to fulfill this need.
In accordance with the present invention there is provided a medical monitoring apparatus that comprises a support member that is adapted for chronic implantation at a predetermined location within the vascular system of a living human or other animal. One or more sensor devices are affixed to the support means for sensing at least one measurable physiologic parameter. The apparatus further includes a means for telemetrically transmitting signals representative of the sensed parameter percutaneously to an external signal receiver. In accordance with one embodiment of the invention, the support means may comprise a self-expanding or balloon expandable tubular stent that is adapted for chronic implantation at a predetermined location in the vascular system and affixed to the tubular stent is an electronic circuit for measuring a physiologic parameter. The electronic circuit means also includes a means for telemetrically transmitting signals representative of the sensed parameter percutaneously to a signal receiver external to the body of the living animal.
To measure left ventricular pressure/temperature, the apparatus of the present invention may be placed in an puncture made through the ventricular septum with the stent being anchored in this opening, such that the pressure/temperature sensor is exposed to blood or tissue in the left ventricle. An anchoring arrangement is provided on the stent to prevent the normal pumping action of the heart from displacing the implanted stent. To prevent blood flow through the tubular stent, the lumen thereof may be packed with a fibrous material for occluding the opening. The electronics module may also be located in the lumen if occlusion is desired.
If the stent device is to be placed in the pulmonary or some other artery of a patient, the anchoring means may comprise a series of hooks that become engaged with the inner wall of the artery when the stent is allowed to or made to expand radially during its implantation.